1. Field of the Invention
This invention relates to an apparatus such as a belt sander. Structures of this type generally comprise opposed rolls which support an endless belt. A drive motor or the like is provided, and the motor may be directly associated with the structure to provide a portable apparatus.
The invention is more particularly concerned with means for maintaining the belt in proper alignment during use of the apparatus. Thus, it has been recongized that the endless belts employed tend to "wander" in one direction or the other during use, and the belt as well as the apparatus can be damaged if this is not controlled.
2. Description of the Prior Art
Structures such as belt sanders have been provided which include at least one adjustable roll so that the tendency for a belt to wander can be controlled to some extent. For example, if an operator observes belt movement, the apparatus can be turned off, and the adjustable supporting roll tilted to compensate for the tendency to wander. This can be an effective technique once the proper adjustments have been made; however, it is time-consuming and readjustments are frequently required in view of the rough handling which characterizes use of the apparatus.
Various attempts have been made to provide automatic belt centering means. Disclosures of structures developed by the prior art are set forth in the following patents:
Dugle, et al. U.S. Pat. No. 2,733,555 PA0 Lubas U.S. Pat. No. 3,029,568 PA0 Murschel U.S. Pat. No. 3,094,819 PA0 Przygocki U.S. Pat. No. 3,665,650 PA0 Bradbury, et al. U.S. Pat. No. 3,789,552 PA0 Van der Linden U.S. Pat. No. 3,900,973 PA0 Habeck, et al. U.S. Pat. No. 3,971,166
Murschel discloses a sanding machine which includes a pivotally mounted roller with guide rods for engaging opposite edges of the belts. Rocking movement of the roller supporting shaft is developed in response to belt edge engagement with the guide rods.
Dugle, et al. described a servo-tracking device which includes a finger 30 and tracking shoe 20 connected to a servo-mechanism. The tracking shoe is tilted in response to belt shifting from a desired position. Przygocki discloses a pneumatic system for oscillating the endless belt transversely of the rollers. An air stream directed against the moving belt edge acts as a sensor for determining edge variations.
The other references referred to are of general interest and are not considered as pertinent as the references described.